Electronic devices, to be serviceable under a wide variety of environmental conditions, must be able to withstand moisture, heat and abrasion, among other stresses. A significant amount of work has been reported directed toward various protective measures to minimize the exposure of these devices to the above conditions and thereby increase their reliability and life. Most of these measures, however, suffer from various drawbacks.
For instance, early measures involved potting electronics within a polymeric resin and, thereby, reducing environmental exposure, These methods proved to be of limited value, however, since most resins are not impermeable to environmental moisture and they generally add extra size and weight.
A second method of protection involves sealing the device within a ceramic package. This process has proven to be relatively effective in increasing device reliability and is currently used in select applications. The added size, weight and cost involved in this method, however, inhibits widespread application in the electronic industry.
Recently, the use of lightweight ceramic coatings has been suggested. For instance, Haluska et al. in U.S. Pat. Nos. 4,749,631 and 4,753,856, which are incorporated herein in their entirety by reference, disclose silicon containing coatings produced by applying solutions of silicon alkoxides or silicon alkoxides and metal oxide precursors, respectively, to an electronic device and then ceramifying by heating to temperatures of 200.degree.-1000.degree. C. These references also describe the application of other coatings containing silicon carbide, silicon nitride or silicon carbonitride onto the initial silica layer for added protection. The ceramic coatings produced thereby have many desirable characteristics such as microhardness, moisture resistance, ion barrier, adhesion, ductility, tensile strength and thermal expansion coefficient matching which provide excellent protection to the underlying substrate.
Despite the efficacy of the above coatings, ceramification at temperatures less than 400.degree. C. is so slow that commercial application is impractical. Moreover, ceramification at temperatures in excess of 400.degree. C. often results in the destruction of many temperature sensitive devices. Therefore, a need exists for a method of rapidly applying ceramic coatings from silicon alkoxides at low temperature.
Chemical vapor deposition of SiO.sub.2 films from silicon alkoxides and ozone is well known. (See, for example CA 88:109402a and CA 105:124,818) These references, however, do not describe the solution coating method claimed herein.
The use of ozone as a method for low temperature conversion of hydrogen silsesquioxane preceramic solution to a ceramic coating has recently been disclosed by Haluska et al. in co-pending application Ser. No. 07/312,457, which is incorporated herein in its entirety by reference. This application, however, does not disclose the use of ozone with silicon alkoxides.
The present inventor has discovered that a ceramic coating derived from a preceramic solution of silicon alkoxides and, optionally, ceramic oxide precursors can be rapidly applied to various substrates at temperatures as low as 40.degree. C. when the ceramification is conducted in an ozone environment.